1. Field of the Invention
The present invention relates to the manufacturing of a semiconductor device, and more particularly to a method of sealing the semiconductor device and the resulting sealed product.
2. Description of the Prior Art
As is well known, when a semiconductor device is used in a high temperature atmosphere or a high humidity atmosphere, it suffers such adverse effects that the electrical characteristics are degraded or that the electrode or connector is disconnected.
For example, when water adheres to an electrode 2 on a semiconductor substrate 1 as shown in FIG. 1, it is ionized on account of the temperature of the atmosphere in which the semiconductor device is used. Under the action of the ions, the bent protruding portion 3 of the electrode 2 or the connecting portion 5 between a bonding wire (connector) 4 and the electrode 2 is corroded.
The portion thus corroded is thinner than the other portions, and generates heat by the flow of a current. Finally, it is disconnected to render the device inferior.
When the ions accumulate on an exposed protective film (SiO.sub.2) designated by reference numeral 6, they gradually invert the conductivity type in the surface portion of a collector region 7 from the side of a base region 8 and thus form a channel. As the ions accumulating on the protective film 6 increase, the channel grows. Eventually, it reaches the peripheral wall of the semiconductor substrate 1, and a leakage current flows to degrade the characteristics of the semiconductor device.
In order to prevent the adverse effects noted above, there has been adopted a method in which the semiconductor element is covered with a resin. With this method, however, the adverse effects cannot be perfectly eliminated.
In this respect, the inventors analyzed the states within the resins in resin-sealed type semiconductor devices, and have found the following facts:
Notwithstanding that an epoxy resin, a silicone resin or the like, which is generally employed, contains no chlorine (Cl) in its molecular structure, chlorine ions (Cl.sup.-) are found in such resin coverings.
Since chlorine exists in any place in the form of a simple substance or compounds, chlorine will adhere to a mix into the resin in the process of producing each resin or in the process of assembling the semiconductor device.
The chlorine is ionized under the influence of, for example, an electric field. The chlorine ions migrate within the resin, accumulate in an electrode portion or a bonding wire, and corrode it. Further, the ions accumulate on a protective film, generate a leakage current by the foregoing phenomenon, and cause the degradation of the characteristics of the semiconductor device.